Bedknife for reel cutting unit and manufacturing method for same

ABSTRACT

A method of manufacturing a bedknife for a reel cutting unit comprises providing a base having a tool steel insert that forms a cutting edge of the bedknife. The base comprises a heat treatable steel. Both the base and the insert are heat treated prior to joining the insert to the base. The insert is then integrally joined to the base by brazing the two together using a silver based filler between the two.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/698,292filed Jan. 25, 2007.

TECHNICAL FIELD

This invention relates generally to a reel mower having a reel cuttingunit. More particularly, this invention relates to the bedknife used onthe reel cutting unit.

BACKGROUND OF THE INVENTION

Reel mowers are well known pieces of outdoor power equipment used forcutting grass. Reel mowers are so named because they have at least onereel cutting unit that includes a bladed reel that rotates about agenerally horizontal axis. Usually the blades of the reel are notthemselves sharpened though in some instances they have been known to besharpened. The primary purpose of the blades of the reel is to sweep theblades of uncut grass against the leading edge of a bedknife that isfixed on the frame of the reel cutting unit. The interaction between theblades of the reel and the bedknife shears the grass blades to cut thegrass.

The geometry of a typical reel cutting unit usually places the bedknifebeneath the rotatable reel and behind the centerline of the reel. Inorder to be effective in cutting grass, the reel and bedknife areadjusted so that the blades of the reel are either immediately adjacentto or in slight contact with the bedknife as the reel rotates. Thisprovides a scissors type shearing action between the reel and thebedknife that is effective for cutting grass.

Many conventional bedknives are integrally formed from a single piece ofsteel that is then heat treated to increase hardness and durability. Thetip of the bedknife is often sharpened to provide a cutting edge.Traditionally, such bedknives are quite strong and resistant to breakingfrom impact. However, such monolithic steel bedknives typically wearfairly quickly, requiring the cutting edge to be resharpened or thebedknife to be replaced. This is a disadvantage to single piecebedknives of this type.

Other known bedknives attempt to improve upon the wearability of singlepiece bedknives. These other bedknives typically comprise a base thatcarries an insert at the tip thereof with the insert forming the cuttingedge of the bedknife. In known insert bedknives, the base materialcomprises a less expensive, non-hardenable, low carbon steel (such asSAE 1018 or 1020). The insert comprises a much more expensive tool steel(such as M2). Neither the base material nor the tool steel are heattreated prior to their being joined together.

In manufacturing such insert bedknives, the base is provided with a seatat the tip thereof to receive the insert. The insert is placed into theseat with a copper brazing alloy being used at the interface between theinsert and the seat. The insert is then brazed into place to integrallyjoin the insert to the base by heating the copper filler at relativelyhigh temperatures of approximately 2000° F. or so. This heating processboth joins the insert to the base as well as heat treats the insert insitu to increase the hardness of the insert. This heating process doesnot, however, appreciably strengthen or harden the base material due tothe fact that the base material is substantially non-hardenable evenwhen heat is applied.

The Applicants herein have observed that conventional insert bedknivesmade as described above have relatively low yield strength in the basematerial. Yield strength is defined as the amount of force required topermanently deform the bedknife. As a result of this low yield strength,the Applicants herein have further observed two failure modes forconventional bedknives.

In the first failure mode, the bedknife strikes foreign objects duringoperation of the reel cutting unit, including but not limited to treeroots, drainage grates, bolts lying on the ground, yardage markers, etc.The impact with foreign objects is often significant to cause thebedknife to chip or fracture. This requires that the bedknife berepaired or even replaced if the area that is damaged is too large. Thisfailure mode contributes to decreased customer satisfaction and higherwarranty costs to the manufacturer of the reel cutting unit.

In the second failure mode, the bedknife can sometimes be deflectedupwardly so that it interferes with the blades of the spinning orrotating reel. When a given blade then comes into contact with orstrikes the bedknife, it is possible to peel off a portion of the hardedge of the bedknife. This is particularly true for bedknives that areextremely thin, such as those used on the reel cutting units ofgreensmowers. Such an occurrence completely destroys the bedkniferequiring that the bedknife be totally replaced. It also cansignificantly damage the rotatable reel, further leading to other repairor replacement costs in conjunction with the reel.

Accordingly, there is a need in the reel mower art for a bedknife baseor body with improved yield strength to minimize the aforementionedfailures described above.

SUMMARY OF THE INVENTION

One aspect of this invention relates to a bedknife for a reel cuttingunit of a reel mower, the bedknife cooperating with a plurality ofblades of a rotatable cutting reel such that grass is pushed against acutting edge of the bedknife by the blades of the rotatable cutting reelto cut the grass by shearing the grass between the cutting edge of thebedknife and the reel blades, the bedknife further having a base with aninsert fitted or secured to the base in a seat at a leading edge of thebase such that the insert forms the cutting edge of the bedknife. Thebedknife comprises a base formed from a heat treatable steel having atleast 30 points of carbon content with the base having a hardness ofapproximately 30 HRC or above. An insert formed from a tool steel isprovided having a hardness of approximately 50 HRC or above. A filler isplaced between the base material and the insert with the filler meltingand flowing upon the application of sufficient heat to integrally jointhe insert and the base material together as a single, integral unitafter the filler solidifies during subsequent cooling. The filler has amelting temperature that is equal to or less than approximately 1300° F.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described hereafter in the Detailed Description,taken in conjunction with the following drawings, in which likereference numerals refer to like elements or parts throughout.

FIG. 1 is a perspective view of a bedknife according to this invention,the bedknife being used on a reel cutting unit of a reel mower; and

FIG. 2 is a longitudinal cross-sectional view through the bedknife ofFIG. 1.

DETAILED DESCRIPTION

FIGS. 1 and 2 show a bedknife for a reel cutting unit of a reel mowerwith the bedknife being generally illustrated as 2. Bedknife 2 iselongated and includes a base 4 having a front tip that includes anL-shaped, upwardly facing shelf or seat 6. An insert 8 is located inseat 6 and forms the cutting edge of bedknife 2. The rear of bedknife 2includes a plurality of holes 10 for mounting bedknife 2 to the bedbarof a reel cutting unit (not shown) of a reel mower (not shown). When somounted, bedknife 2 underlies a portion of the rotatable reel (notshown) of the reel cutting unit with insert 8 closely approaching oreven slightly touching the orbit of the blades of the rotatable reeldepending upon the degree of desired adjustment between bedknife 2 andthe reel. The structure per se of 2 bedknife as depicted in FIGS. 1 and2 is generally conventional, i.e. prior art bedknives look the same aswhat is shown in FIGS. 1 and 2.

This invention relates to the selection of various materials for use inbase 4 and insert 8 of bedknife 2, to the treatment of these materialsprior to their being joined together, and to how these materials arejoined together to form a completed bedknife, i.e. to the method ofmanufacture of a new and improved bedknife. This invention also relatesto the new and improved bedknife so formed and manufactured.

This invention relates to the use of a heat treatable steel as thematerial of base 4 and the use of a tool steel (such as M Series toolsteels)) as the material for insert 8. The steel used as the basematerial comprises heat treatable structural or spring steel or coldworked steel with similar strength and hardness properties. The toolsteel is preferably wear resistant. Both the base material and insert 8are heat treated to increase their hardness prior to their being joinedtogether with the base material preferably being treated to at leastapproximately 30 HRC and the tool steel preferably being treated to atleast approximately 50 HRC on the Rockwell hardness scale.

Preferably, the base material has at least 30 points of carbon orhigher. One material that has been used as the base material is an SAE1566 steel having 66 points of carbon. The base material must haveenough carbon that it will become substantially harder with theapplication of heat so that it is now possible to effectively heat treatthe base material because of the higher carbon content of the steel usedin the base material as compared to the lower carbon steels used in thepast (i.e. the steels having only 18 or 20 points of carbon).

In joining base 4 and insert 8 together, insert 8 is placed in seat 8 atthe tip of base 4 with a silver based filler being used at the interfacebetween seat 8 and insert 8, i.e. along the two sides of insert 8 thatcontact or abut with the L-shaped seat 6. The method of manufacture thenconcludes by brazing insert 8 to base 4 at a lower temperature than withprior art bedknives. Because of the use of a silver based material asthe filler instead of copper, insert 8 can be brazed onto base 4 byheating at approximately 1150-1200° F. rather than at 2000-2100° F. withprior art bedknives. Materials that are not silver based could be usedas the filler provided that the melting temperatures of such filler arelower than approximately 1300° F.

The Applicants have found that this manufacturing method provides abedknife with much improved yield strength in the base material. Insert8 and base 4 are both heat treated prior to their being joined together.However, when being joined together, the brazing process is done at amuch lower temperature, e.g. at or less than 1300° F. such as the1150-1200° F. needed for a silver based filler rather than at 2000-2100°F. The brazing step also preferably takes place uniformly using aconstant brazing temperature and time without trying to braze at muchhigher temperatures for shorter periods of time. This lower temperaturedoes not appreciably temper either the tool steel used in insert 8 orthe heat treated base material since high speed steels and conventionalheat treatable steels both temper quickly above 1300° F. but not belowthis temperature. This avoids appreciably weakening the strengthpreviously provided in the base material by the heat treating step doneprior to insert 8 and base 4 being joined together. Thus, the brazingstep does not significantly lower the yield strength of the basematerial of bedknife 2.

Accordingly, bedknife 2 of this invention is significantly moreresistant to damage than prior art insert bedknives because its yieldstrength is considerably improved. Impacts with tree roots, drainagegrates, or other objects are much less likely to chip or break bedknife2. In addition, should bedknife 2 deflect up into closer contact withthe blades of the cutting reel, the reel blades are far less likely topeel portions of bedknife 2 into the reel. In fact, the Applicants haveobserved that bedknife 2 is strong enough to often simply stop or jamthe rotation of the cutting reel when bedknife 2 is struck by a blade ofthe cutting reel. In the past, such impacts would have broken bedknife 2and peeled portions of bedknife 2 into and through the reel, damagingboth bedknife 2 and the cutting reel. Now, damage is avoided to thecutting reel and bedknife 2 is either undamaged or sufficiently lightlydamaged so as to be easily repairable.

Various modifications of this invention will be apparent to thoseskilled in the art. Accordingly, this invention is to be limited only bythe appended claims.

1. An improved bedknife for a reel cutting unit of a reel mower, thebedknife cooperating with a plurality of blades of a rotatable cuttingreel such that grass is pushed against a cutting edge of the bedknife bythe blades of the rotatable cutting reel to cut the grass by shearingthe grass between the cutting edge of the bedknife and the reel blades,the bedknife further having a base with an insert fitted or secured tothe base in a seat at a leading edge of the base such that the insertforms the cutting edge of the bedknife, which comprises: (a) a baseformed from a heat treatable steel having at least 30 points of carboncontent with the base having a hardness of approximately 30 HRC orabove; (b) an insert formed from a tool steel having a hardness ofapproximately 50 HRC or above; and (c) a filler placed between the basematerial and the insert with the filler melting and flowing upon theapplication of sufficient heat to integrally join the insert and thebase material together as a single, integral unit after the fillersolidifies during subsequent cooling, wherein the filler shall have amelting temperature that is equal to or less than approximately 1300° F.2. The bedknife of claim 1, wherein the filler is silver.